Thorax in winged Insects. 151 



last number of segments. I even stated some strong arguments for think- 

 ing that the Ametahola and Arachnida might be reduced to the annulose 

 type of form. Such was the state of the subject when I left it. I now 

 therefore proceed to M. Audouin's general theory of the insect skeleton 

 which is the same precisely as mine, although, from his taking no notice 

 of my work in the" Annales dea Sciences JVaturelles,^'' I must suppose he 

 never saw it. By a cautious process of induction he says that he has 

 arrived at the following important conclusions, viz. 



1st. That the skeleton of annulose animals is formed of a determinate 

 number of parts, which are either distinct or confluent, as may be, but 

 which exist generally in all. 



2ndly. That in some cases a part will be diminished, or even will 

 disappear, while in others the same piece will undergo an extraordinary 

 developement. 



3rdly. That the developement of one piece exerts an inverse influence 

 on the contiguous pieces, whence arise the principal differences so much 

 rehed upon in classification. 



With respect to these three results I may observe, that they are in 

 perfect accord with the "Hors EntomologiccB.'' I had alreadyin that work 

 stated the determinate number of primary segments to which the Verte- 

 bral Axis of all annulose animals tended, and as to M. Audouin's second 

 conclusion, it is nothing more than another mode of expressing the 

 maxim of variation as applied to organs. His two leading observations, 

 therefore, that the skeleton of Crustacea and Arachnida only differs from 

 that of Winged Insects by the mode in which their segments are developed, 

 and that the Annulosa generally only differ from each other in the deve- 

 lopement of the same parts in each, or in the confluence or separation of 

 these parts, are neither of them new, any more than the reduction of the 

 larva and perfect insect to the same general law of structure. Where we 

 differ is, as to the mode in which this reduction may be made, and I 

 confess, after having bestowed some attention on the subject, that I am 

 inclined now to prefer the explanation given by M. Audouin. Our 

 leading principles are, however, nearly the same, and in fact, as the 

 study of the natural system is founded on the maxim of variation,* so that 



* The maxim of variation, as applied to the arrangement of the animal 



